The present invention relates to domestic hot water heaters, and in particular, to combination units that use part of the hot water heated by these heaters for space heating purposes.
Most buildings that require a domestic or potable hot water supply as well as space heating use separate devices for each purpose. For example, a typical house has a domestic hot water heater with its own water tank and burner or electric element to heat the water in the tank. If heating is required, a separate furnace or space heater is employed. This room air heater again has its own burner or electric heating element. This is inefficient and wastes energy and is unnecessarily expensive due to the duplication of equipment.
Attempts have been made in the past to overcome some of these inefficiencies by trying to use a single burner or heat source for both the domestic hot water and space heating requirements. So called combination units have been produced which are basically conventional domestic water heaters. When there is no demand for the heated potable water, rather than have the water tank sit idle wasting energy through heat loss, the hot water is circulated through a heat exchanger mounted in an air handler or blower and thus used to heat the air space.
Examples of the above-mentioned combination units are disclosed in Canadian patents Nos. 2,002,488 issued Nov. 11, 1994 and 2,033,415 issued May 3, 1994, and also in U.S. Pat. Nos. 4,925,093 issued May 15, 1990 and 5,074,464 issued Dec. 24, 1991. A difficulty with these prior art combination units, however, is that the heat exchangers reduce the temperature of the water in the water tanks so much that there is either an inadequate supply of hot water when it is required, or the air that is heated by the heat exchanger is at so low a temperature that it is uncomfortable. As a result, neither the hot water heating nor the room air heating is satisfactory and the units are not generally accepted in the marketplace.
The present invention keeps the temperature drop of the water passing through the heat exchanger low enough not to interfere with the supply of domestic hot water, yet provides an ample flow rate through the heat exchanger to provide ample hot air at a comfortable temperature adequate to meet the room air heating requirements.